Portable electronic apparatuses, such as cellular phones and notebook computers, have become smaller and thinner while the amount of heat generated in large-scale integration (LSI) circuits has increased.
To suppress a temperature rise on the housing surface of such an apparatus, a heat diffusing sheet with high heat conductivity and low thickness, such as a graphite sheet or a metal leaf, has been used for diffusing heat in the operation unit or display unit only. However, in recent years, due to a further increase in power consumption and a further reduction in thickness and substrate area of cellular phones, the heat density of cellular phones have increased. As a result, it has become difficult to achieve sufficient cooling in a cellular phone by heat diffusion performed only in the operation unit or display unit of the cellular phone.